Search

An extraction technique for flat band voltage (${V}_{\textit {FB}}$) in an amorphous InGaZnO (a-IGZO) thin-film transistor (TFT) using the frequency-independent ${C}-{V}$ relationship which is taken from the measured multi-frequency ${C}-{V}$ characteristics, is proposed. The proposed method comprises the consideration of multiple physical parameters for accurate ${V}_{\textit {FB}}$ extraction, including the sub-gap density of states, doping concentration, gate oxide capacitance, and series resistance. The method was verified by comparing both the measured current–voltage characteristics and the extracted ${V}_{\textit {FB}}$ value with the technology computer-aided design simulation results. Moreover, we confirmed the versatility of the method by extracting ${V}_{\textit {FB}}$ from devices with different oxygen contents. The proposed physical-based technique showed better accuracy and compatibility with amorphous oxide semiconductor (AOS) TFTs compared with classical empirically based methods. We believe that our technique is useful for the experimental design and optimization of the gate metal-dielectric-AOS stack for high-performance AOS TFTs. [ABSTRACT FROM AUTHOR]

The instability induced under positive gate-bias stress (PBS) in amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) with self-aligned top-gate coplanar structure is investigated under the threshold-voltage $({V}_{T})$ compensated pixel scheme in the backplane of organic light-emitting diode displays and compared with that under a constant-PBS scheme. Based on the investigation, which combines the extraction of density of states, the decomposition of ${V}_{T}$ shift ($\Delta {V}_{T}$), and technology computer-aided design, the unreleased electric field across the gate insulator (GI) and the maintained electron concentration are observed under the ${V}_{T}$ -compensated PBS condition. Indeed, the main difference between the two schemes originates from increasingly activated electron trapping within the GI deep-level traps and from the excessive oxygen-related peroxide bond-breaking in the a-IGZO-active film, i.e., O22− + $2 {e}^{-} \to$ O2− + O2−. Although the latter is quantitatively much smaller than the former, the two mechanisms are closely related to each other and should be jointly optimized. This is because a large amount of oxygen interstitials can generate a high density of GI electron traps. Since the GI deep-level trapping results in noticeable $\Delta {V}_{T}$ with an increase in PBS time, our results suggest that the $\Delta {V}_{T}$ should be seriously underestimated with respect to either the estimation of pixel lifetime or the assessment of ${V}_{T}$ -compensated pixel-circuit schemes, if the reliability/acceleration test relies only on the constant-PBS-based single-TFT device test. [ABSTRACT FROM AUTHOR]